Normal anatomic relationships of the craniocervical junction on MDCT in 200 patients and comparison with accepted values on plain radiographs*
| Method | Mean | SD | Range | MDCT Normal Value† | Plain Radiograph Normal Value2,5,6 |
|---|---|---|---|---|---|
| BAI | 3.4 | 4.64 | −8.7–26.0 | Not reliable | <12.0 |
| BDI | 5.7 | 1.39 | 1.4–9.1 | <8.5 | <12.0 |
| Powers ratio | 0.8 | 0.08 | 0.6–1.2 | <0.9 | <1.0 |
| ADI | 1.3 | 0.37 | 0.5–2.4 | <2.0 in both sexes | <3.0 men |
| <2.5 women | |||||
| AOI | 1.0 | 0.23 | 0.5–1.8 | <1.4 | No data in adults |
Note:—MDCT indicates multidetector row CT; BAI; basion-axial interval; BDI, basion-dens interval; ADI, atlantodental interval; AOI, atlanto-occipital interval.
* Results are given in millimeters with the exception of the Powers ratio.
† Normal value is the maximum value for 97.5% of the population.